220 CORDAITEAE [CH. 



application of the generic name Cordaites. It has been the general 

 practice to apply this name to certain forms of linear leaves 

 which are particularly abundant in Carboniferous and Permian 

 strata in Europe and North America, and in recent years a few 

 palaeobotanists have substituted Cordaites for Noeggerathiopsis 

 as the more suitable designation for Permo-Carboniferous specimens 

 abundant in the rocks of Gondwana Land. It has been customary 

 to assign to Cordaites certain reproductive shoots, seeds, and 

 stems described under the generic names Cordaianthus, Cordai- 

 carfus, Cordaicladus, Cordaioxylon, etc. Stems agreeing anatomi- 

 cally in their main features with those of recent Araucarineae 

 have loiig been attributed to Cordaites, but a few years ago a new 

 type of stem was discovered which, though almost identical 

 with that of Cordaites, is distinguished by the character of the 

 primary xylem. For this new type the name Mesoxylon^ was 

 proposed. Nothing is known as to the reproductive organs borne 

 on Mesoxylon stems, but the leaves are externally at least indis- 

 tinguishable from those referred to Cordaites. It is therefore 

 obvious that when we apply the name Cordaites to leaves or 

 other plant-organs, under that designation are undoubtedly 

 included specimens belonging both to Mesoxylon stems and to 

 stems with the characters of Cordaites (Cordaioxylon). Further 

 research may enable us to subdivide Cordaites into more pre- 

 cisely defined types distinguished by well-marked morphological 

 characters, but at present the onh^ course would seem to be to 

 restrict the term Mesoxylon to petrified stents exhibiting the 

 features of that genus and to retain Cordaites as a comprehensive 

 designation in accordance with the general account of the genus 

 given in the following pages. This widely distributed and mainly 

 Palaeozoic genus is especially well represented in the coalfields 

 of France where in some localities it contributed largely to the 

 formation of seams of coal^, and it is chiefly from the researches 

 of French Palaeobotanists that our knowledge of its morphology 

 is derived. Cordaites has shared the fate of most other abundant 

 fossil plants in the distribution of its disjuncta membra among 

 several genera and classes, but on the whole the information that 



' See page 270. ^ See Vol. i. p. 76, fig. 13. 



